The field of the disclosure relates generally to capacitive sensors, and more specifically, to a capacitive sensor device and method of manufacturing the same for measuring clearance between two objects.
Various types of sensors are used to measure distance between objects in various applications. For example, in turbo machinery applications, such as turbine systems, the clearance between a static shroud and turbine blades may be measured using a sensor disposed within the turbine. The clearance is greatest when the turbine is cold, and gradually decreases as the turbine heats up and as it spins up to speed. It is desirable that a gap or clearance between the turbine blades and the shroud be maintained for safe and effective operation of the turbine. The measured distance may be used to direct movement of the shroud to maintain the desired displacement between the shroud and the turbine blades.
In some applications, capacitance probe sensors are employed to measure the distance between two objects. Typically, when such sensors are placed in high temperature environments, a signal processing unit of a sensor is required to be located in an ambient environment at a distance from the probe. Normal turbo machinery has a temperature gradient that reduces with a radial distance from a gas flow path contained within the shroud. In corrosive and/or high temperature gas flow paths, such known sensors have a limited lifetime, for example 100-500 hours as compared to the lifetime of the turbines in which they are installed, which may be multiple thousands of hours. Over time, the high temperature and corrosive gas flow paths may cause cracks in probe tips and/or insulation of the sensors, enabling moisture ingress into the sensor tip cavity and subsequent degradation.